feature: NetworkWriter.WriteBytes(byte*) unsafe version to prepare for BitTree delta compression

Assets/Mirror/Core/NetworkWriter.cs

@@ -197,6 +197,26 @@ public void WriteBytes(byte[] array, int offset, int count)
             Array.ConstrainedCopy(array, offset, this.buffer, Position, count);
             Position += count;
         }
+        // write an unsafe byte* array.
+        // useful for bit tree compression, etc.
+        public unsafe bool WriteBytes(byte* ptr, int offset, int size)
+        {
+            EnsureCapacity(Position + size);
+
+            fixed (byte* destination = &buffer[Position])
+            {
+                // write 'size' bytes at position
+                // 10 mio writes: 868ms
+                //   Array.Copy(value.Array, value.Offset, buffer, Position, value.Count);
+                // 10 mio writes: 775ms
+                //   Buffer.BlockCopy(value.Array, value.Offset, buffer, Position, value.Count);
+                // 10 mio writes: 637ms
+                UnsafeUtility.MemCpy(destination, ptr + offset, size);
+            }
+
+            Position += size;
+            return true;
+        }
 
         /// <summary>Writes any type that mirror supports. Uses weaver populated Writer(T).write.</summary>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]

Assets/Mirror/Tests/Editor/NetworkWriterTest.cs

@@ -133,6 +133,22 @@ public void TestWritingBytesSegment()
                 Assert.That(deserialized.Array[deserialized.Offset + i], Is.EqualTo(data[i]));
         }
 
+        [Test]
+        public unsafe void WriteBytes_Ptr()
+        {
+            NetworkWriter writer = new NetworkWriter();
+
+            // make sure this respects position & offset
+            writer.WriteByte(0xFF);
+
+            byte[] bytes = {0x01, 0x02, 0x03, 0x04};
+            fixed (byte* ptr = bytes)
+            {
+                Assert.True(writer.WriteBytes(ptr, 1, 2));
+                Assert.True(writer.ToArraySegment().SequenceEqual(new byte[] {0xFF, 0x02, 0x03}));
+            }
+        }
+
         // write byte[], read segment
         [Test]
         public void TestWritingBytesAndReadingSegment()